USDA zone 4b in Maine
USDA plant hardiness zone 4b covers 17 locations across Maine (average annual extreme minimum −25 to −20 °F): Ashland, ME, Danforth, ME, Eagle Lake, ME, Fort Kent, ME, Greenville, ME, Greenville, ME, and 11 more. Average last spring frost across this group ranges May 6 (Madawaska) to June 2 (Eagle Lake), and growing seasons run 102–153 days (Eagle Lake to Greenville) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Maine location's own frost dates; the printable planting calendar uses Houlton, this group's median-season location.
- USDA zone
- 4b−25 to −20 °F
- Last frost range
- May 6–Jun 2avg, 32°F
- First frost range
- Sep 15–Oct 9avg, 32°F
- Growing season range
- 102–153days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Ashland | Blaine | Bridgewater | May 25 | Sep 18 | 115 |
| Danforth | — | Danforth | May 25 | Sep 24 | 119 |
| Eagle Lake | — | Allagash | Jun 2 | Sep 15 | 102 |
| Fort Kent | — | Ft Kent | May 23 | Sep 24 | 121 |
| Greenville | — | Greenville Maine Forestry Svc | May 7 | Oct 9 | 153 |
| Greenville | — | Brassua Dam | May 23 | Sep 29 | 128 |
| Greenville | — | Jackman | May 26 | Sep 23 | 119 |
| Houlton * | — | Houlton 5n | May 19 | Sep 23 | 125 |
| Houlton | Oakfield | Houlton Intl Ap | May 27 | Sep 18 | 115 |
| Kingfield | — | Long Falls Dam | May 13 | Sep 30 | 138 |
| Kingfield | Rangeley | Eustis | May 24 | Sep 21 | 118 |
| Madawaska | Grand Isle | Frenchville Aroostook Ap | May 6 | Oct 2 | 147 |
| Newport | Corinna | Corinna | May 8 | Oct 3 | 148 |
| Oakfield | Patten, Island Falls | Patten 2 | May 13 | Sep 30 | 138 |
| Rangeley | — | Rangeley | May 23 | Sep 27 | 127 |
| Rangeley | — | Rangeley 2 Nw | May 23 | Sep 24 | 123 |
| Rumford | Rangeley | Middle Dam | May 19 | Oct 1 | 133 |
* Houlton is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Houlton, representative)
Computed from Houlton's average frost dates — the median-season location in this Mainezone 4b group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Mar 24 – Apr 7 | May 26 – Jun 2 | Jul 25 – Aug 14 | — | matures comfortably |
| Pepper | Very tender | Mar 10 – Mar 24 | Jun 2 – Jun 9 | Aug 1 – Aug 31 | — | matures comfortably |
| Cucumber | Tender | Apr 21 – Apr 28 | May 26 – Jun 2 | Jul 15 – Aug 4 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 26 – Jun 2 | Jul 10 – Jul 25 | — | matures comfortably |
| Bush bean | Tender | — | May 26 – Jun 2 | Jul 15 – Jul 25 | Jul 25 – Aug 4 | matures comfortably |
| Sweet corn | Tender | — | May 19 – Jun 2 | Jul 18 – Aug 17 | — | matures comfortably |
| Basil | Very tender | Apr 7 – Apr 21 | May 26 – Jun 2 | Jun 25 – Jul 10 | — | matures comfortably |
| Lettuce | Half-hardy | Apr 7 – Apr 21 | Apr 21 – May 5 | Jun 5 – Jun 20 | Jul 11 – Jul 26 | matures comfortably |
| Pea | Hardy | — | Apr 7 – Apr 21 | Jun 1 – Jun 16 | Jul 1 – Jul 16 | matures comfortably |
| Spinach | Hardy | — | Apr 7 – Apr 21 | May 17 – May 27 | Jul 21 – Jul 31 | matures comfortably |
| Carrot | Half-hardy | — | Apr 28 – May 5 | Jun 27 – Jul 17 | Jun 21 – Jul 11 | matures comfortably |
| Broccoli | Half-hardy | Mar 24 – Apr 7 | Apr 21 – May 5 | Jun 15 – Jul 5 | Jun 26 – Jul 16 | matures comfortably |
Which crops fit this growing season
Using Houlton's own 125-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Houlton)
From NOAA's 1991–2020 Climate Normals at station USC00173944. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | Jun 1 | Jun 16 | Sep 10 | Sep 24 | 101 |
| 32°F (freeze) | May 19 | Jun 2 | Sep 23 | Oct 7 | 125 |
| 28°F | May 4 | May 18 | Oct 5 | Oct 23 | 151 |
| 24°F | Apr 25 | May 7 | Oct 19 | Nov 5 | 177 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 17 locations is 1,613; Houlton's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 1,808 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 3,547 | cool-season crops (brassicas, greens) |
Hardiness zone 4b in Maine
Zone 4b means an average annual extreme minimum winter temperature of about −25 to −20 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Maine spans 8 hardiness zones in this dataset — see all Maine locations for the full range, including zones3b, 4a, 5a, 5b, 6a, 6b, 7a.
Explore zone 4b in other states at zone 4b, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 4b mean in Maine?
- Zone 4b means an average annual extreme minimum winter temperature of −25 to −20 °F — the standard USDA measure of which perennials survive winter. 17 locations in Maine fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Maine's zone 4b is the growing season longest?
- Greenville runs the longest season on this page at about 153 days; Eagle Lake is shortest at about 102 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Maine's zone 4b?
- Using Houlton's frost dates (this page's median-season location): start seeds indoors about Mar 24 – Apr 7, then transplant outside about May 26 – Jun 2. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Maine's zone 4b have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 17 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.